1. Field of the Invention
The invention relates to a smart card with a card body and a plurality of contact areas formed of electrically conductive material. The contact areas are electrically connected to contact terminals assigned to an electronic circuit formed on the semiconductor substrate of a semiconductor chip. The invention also relates to a semiconductor chip with contact terminals assigned to an electrical circuit formed on the semiconductor substrate of the semiconductor chip.
2. Description of the Related Art
Such smart cards and also semiconductor chips for use in a smart card have been disclosed for example by Rankl and Effing, Handbuch der Chipkarten [Smart card reference book], Carl Hanser Verlag, Munich/Vienna, 1995. According to Rankl and Effing, during the production of smart cards, so-called chip modules were fabricated first of all, the chip modules constituting intermediate products which can be produced as self-contained units in terms of production engineering and can be processed further independently to form end products. A chip module is in that case understood to mean a configuration in which an electrically insulating carrier has arranged on or in it one or more integrated semiconductor circuits in the form of chips or integrated circuits which are connected via connecting terminals to a conductor track system provided on one side or on both sides of the carrier. The carrier generally constitutes a flexible film on which the actual chip is mounted and on which the contact areas of the smart card are situated. The contact areas are usually gold-plated. During the production of such a chip module, essentially two different techniques are used to pack the semiconductor chip onto the carrier film: namely the so-called TAB technique (tape automated bonding) and the wire bonding technique. In the TAB technique, metallic bumps are firstly electrodeposited on the pads of the semiconductor chip, the conductor tracks of the carrier film subsequently being soldered onto the bumps. The soldered joint is mechanically loadable in such a way that the chip itself need not be fixed any further, but rather simply hangs from the conductor tracks. The advantage of the TAB method resides in the high mechanical loadability of the chip connections and in the small structural height of the module. However, this advantage has to be acquired at a greater expense than the wire bonding module. In the case of the latter, a plastic film is once again provided as the carrier material, the gold-coated contact areas being electrodeposited on the front side of the plastic film. Holes are stamped on the carrier film in order to accommodate the chip and the wire connections. The chip is then fixed into the stamped-out portion provided from the rear side on the conductor track (die bonding). The chip terminals are subsequently connected by thin wires (a few micrometers) to the rear side of the contacts. Finally, the chip and the bonding wires are protected against environmental influences by a potting compound. The advantage of this method resides in the fact that this largely follows the method for packaging chips in standard housings which is customary in the semiconductor industry, and it is consequently less expensive. The disadvantage resides in the fact that both the structural height and the length and width of the module are distinctly greater than those of the TAB module, because not only the chip but also the bonding wires have to be protected by the covering compound. This also magnifies the problems, however, when the modules are incorporated in the smart card.
European patent application EP 0 207 852 A1 describes a module that is constructed similarly to a TAB module. There, the semiconductor chip likewise has soldering bumps which are connected to conductor tracks on a carrier film. However, the conductor tracks are in that case pressed by means of a punch in the manner of a deep-drawing process through cutouts in the carrier film, so that they can then be connected to the soldering bumps. That process is very complicated, however. In addition, the soldering bumps must be positioned very accurately in order to ensure a clean connection to the conductor tracks.
The individual chip modules are subsequently stamped from the finished mounted film and introduced into the smart card. In the method, the semiconductor chip is not directly fixed in the card, which has the advantage that the bending forces which arise during mechanical loading of the card are largely kept away from the semiconductor chip. All previously disclosed module construction techniques or housing technologies from the smart card sector share the objective of protecting the integrated circuit against mechanical loading on account of bending or torsion, which can lead to the destruction of the integrated circuit on account of its brittle material properties. The standard thickness of the integrated circuits or semiconductor chips used in smart cards is about 200 .mu.m at the present time. The modulus of elasticity of silicon here is of the order of magnitude of 190.times.10.sup.3 N/mm.sup.2. The material behavior of the silicon chip is thus extremely brittle. Protection of the sensitive semiconductor chip afforded by the housing is cost-intensive owing to the requisite outlay in terms of mounting and material and time-consuming owing to the mounting and production steps to be carried out only after the fabrication of the integrated circuit.